Bicomponent acrylic fiber having modified helical crimp



1 1970 H. A. HOFFMAN, JR 3,547,753

BICOMPONENT ACRYLIC FIBER HAVING MODIFIED HELIGAL CRIMP Filed June 5, 1967 United States Patent O US. Cl. 161173 4 Claims ABSTRACT OF THE DISCLOSURE Bicomponent acrylic fibers which offer advantageous properties in a wide range of knitted and woven fabrics in which each component is selected from the group consisting of (A) polyacrylonitrile, (B) copolymers consisting essentially of at least about 88% by weight acrylonitrile and up to about 12% by weight of at least one member of the group of copolymerizable compounds consisting of addition monomers which are non-ionizing in neutral media and addition monomers bearing sulfonate groups; and (C) mixtures of two or more of said polymers. The polymeric components each have no more than about 90 milliequivalents per kilogram of combined anionic function and are present in a weight ratio of about 75:25 to about 25 :75 in the fiber cross-section. The fiber has a unique modified helical crimp in which the ratio of crimp reversals to crimp frequency (R/F) is in the range of about 0.75 to 1.0.

BACKGROUND OF THE INVENTION A unique bicomponent acrylic fiber is provided which offers advantageous properties in a wide range of knitted and woven fabrics. Its novel crimp configuration yields yarns which are less elastic than the acrylic bicomponent fibers of the art and in which the crimp present contributes more efficiently to yarn and fabric bulk.

Bicomponent acrylic fibers are well-known in the art as exemplified by the Taylor US. Patent No. 3,038,237 and the Belck and Siedschlag U.S. Patent No. 3,039,524. Such fibers comprise along their length two or more eccentrically disposed polymeric materials derived from at least 85% acrylonitrile, which polymers differ in their abilities to shrink. Such fibers, when exposed to conditions which cause them to shrink, will helically crimp to an extent determined by a number of manufacturing and textile processing conditions as well as the composition and ratio in the fiber of the component polymeric materials. The development of crimp has generally been accomplished in a scouring or dyeing operation applied to either textilespun yarn or knitted or woven fabrics. Development of crimp at this late stage of textile processing provides a route to attractive, bulky structures which have excellent tactility and find utility in the manufacture of a variety of fabric types.

For some uses, notably in hand knitting yarns, a lower elasticity is a distinct advantage. Excessive elasticity makes it more difficult to reproduce stitch size and, for all but the most experienced knitters, leads to non-uniform appearance in the final fabric. To a lesser, but still substantial, degree, this difliculty is also seen in knitting on commercial machines. An acrylic bicomponent yarn capable of producing a substantially less elastic yarn without severe loss in bulk would be highly desirable.

SUMMARY OF INVENTION This invention provides a bicomponent acrylic fiber with unique crimp structure. It further provides a bicomponent acrylic fiber capable of conversion to yarns and fabrics of desirable tactility and lower elasticity. Further "ice advantages will become apparent as the description of invention proceeds.

These and other advantages are provided by this invention in a bicomponent acrylic fiber having a cross-section with no more than two axes of symmetry comprising two polymeric components selected from the group consisting of (A) polyacrylonitrile, (B) copolymers consisting essentially of at least about 88% by weight acrylonitrile and up to about 12% by weight of at least one member of the group of copolymerizable compounds consisting of addition monomers which are non-ionizing in neutral media and addition monomers bearing sulfonate groups, and (C) mixtures of two or more: of said polymers, said polymeric components having no more than 90 milliequivalents per kilogram (meq./kg.) of combined anionic function, being present in a weight ratio in the range of /25 to 25/75 in the fiber cross-section, said fiber having a modified helical crimp in which the ratio of crimp reversals to crimp frequency is in the range of 0.75-1.

DESCRIPTION OF DRAWINGS FIG. 1- is a central, cross-sectional elevation of a spinneret assembly which can be used to make the composite filaments of this invention;

FIG. 1A is an enlarged portion. taken from FIG. 1 to show details of the spinneret at the spinning orifice;

FIG. 2 is a transverse, cross-sectional plan view of the apparatus of FIG. 1 taken at 2-2 thereof and showing details of the top back plate;

FIG. 3 is a transverse, cross-sectional plan view taken at 33 of FIG. 1, showing details of the bottom of the back plate;

FIG. 4 is a schematic, enlarged illustration of a crimped bicomponent filament known to the art;

FIG. 5 is a schematic, enlarged illustration of the fiber of this invention; and

FIGS. 6, 7, 8 and 9 represent exemplary fiber crosssections of limited symmetry (i.e., no more than two axes of symmetry) which are useful in the products of this invention.

With reference to FIG. 1, the bottom spinneret plate 2 which contains a circle of orifices 3 is held in place against back plate 1 by retaining rings 12 and 14 and by bolt 13'. A fine-mesh screen 4, e.g. 200 meshes per inch, is placed into position, and serves as a spacer, between spinneret plate 2 and back plate 1. Back plate 1 contains two annular chambers 8 and 9 which are connected to suitable piping and filtration apparatus, not shown, to receive different spinning solutions. Lead holes 11 go from annular chamber 9 to annular space 7. Lead holes 10 lead from annular chamber 8 to annular space 6. Annular spaces 6 and 7 are separated by septum 5 which is disposed above orifices 3 and spaced from spinneret plate 2 by screen 4 to permit free and contiguous passage of the spinning solutions from annular spaces 6 and 7 through orifices 3, the mesh of screen 4 being open enough to permit spinning solution passage to orifices 31 as shown in detail in FIG. 1A.

In FIG. 2 are shown four lead holes 10 and four lead holes 11 equally spaced within the concentric chambers 8 and 9, respectively.

In FIG. 3 are shown the concentric inner and outer annular spaces 6 and 7, sections of bottom spinneret plate 2 and the fine-mesh screen 4 partially in section.

Operation of the described apparatus in the practice of this invention is readily understood. Separate spinning solutions are supplied to the inner annular chamber 9 and outer annular chamber 8, respectively, of the back plate; the former flows from chamber 9 through lead holes I11 into the inner annular space 7 and thence through screen 4 and orifices 3 to form a part of a composite filament,

while the latter passes through the lead holes to the annular space 6 and thence through screen 4 and the outer side of orifice 3 to form the other part of the composite filament.

With reference to FIG. 4, the two components of the bicomponent fiber are schematically identified as shaded and unshaded areas, respectively, representing their relative dispositions in a crimped, bicomponent acrylic fiber generally known to the art. Although reversals in the direction of the spiral occasionally occur in this type of bicomponent fiber, they are infrequent, and the result of an accumulation of torsional strain as the fiber twists under the forces developed by greater shrinkage of component A relative to component B.

FIG. 5 schematically depicts the crimping configuration of the unique product of this invention. It will be seen that the beginning of a crimp in the S direction is present over the length from 14 to 15, but that in the length from 15 and 16 the crimp has a Z-configuration. In the product of this invention, such regular reversals greatly predominate over the regular helical crimp known to the art.

DEFINITIONS AND STANDARDS Intrinsic viscosity, as referred to herein, is measured at C. on a 0.5% solution of the polymer in dimethyl formamide in which has been dissolved 4% lithium bromide.

Helical crimp frequency, F, and crimp reversals, R, are reported on an extended-length basis. The cr-imps of both configurations (i.e., S and Z) are counted, taking a full 360 turn, if such is seen, or whatever portion of a cycle in either configuration which may exist between reversals (i.e., change to the alternate configuration) as one crimp. A reversal is counted for each change in configuration. An arbitrary length of crimped filament is so evaluated and the actual, extended length determined by loading the filament just sufiiciently to remove the crimp. Results are reported as crimps/inch (crimps/cm.), and as the ratio of crimp reversals to crimps, R/ F. It has been found convenient in analyzing these products to randomly select five filaments, lay them across the short dimension of a microscope slide, visually evaluate each filament for crimpand reversals-frequency and subsequently determine the extended length of each of the %-iIlCh crimped lengths of fiber.

The fiber of this invention is seen to have extensive sections substantially as presented in the somewhat idealized schematic FIG. 5. Variations in frequency of crimp occur, however, due to the tendency of any process to introduce minor non-uniformities which can affect crimp. Occasionally, a complete spiral crimp such as presented in FIG. 4 will be seen. In the determination of R/F values, the number of reversals and crimps are tabulated without regard to their relative spacings along the fiber. Crimp Index is calculated as 100 times the ratio of L length of crimped filament is measured under a 2 'mg./ denier load (L It is then measured while under a load just suflicient to remove the crimp (80 mg./denier) (L Crimp Index is calculated as 100 times the ratio of L L0 to L1.

Combined anionic function is determined on the polymers of this invention -by the following procedure:

A l-inch diameter tube equipped with a stop-cock at the lower end and having a total capacity of 500 ml. is charged successively with 200 ml. of dehydrated Amberlite IR-lZO H resin and 200 ml. of Amberlite MB-3 resin so that the MB-3 resin is in the upper part of the column. Both of these resins are available from the Robm and Hass Chemical Company is a water-wet form. [The IR-lZO H resin is a strongly acidic sulphonated polystyrene type resin with exchange capacity of at least 1.7 milliequivalents of cations per milliliter (4.6 milliequivalents per gram). The MB-3 resin in a monobed exchange resin comprising equivalent amounts of lR-lZO H and Amberlite IRA-410 in the fully regenerated form. Total capacity is at least 0.5 milliequivalent per milliliter. IRA-410 is a strongly basic quaternary ammonium polystyrene type resin.] They are dehydrated by slurrying in a flooded bath with dry acetone until no further shrinkage of the resin bed occurs. The acetone is then displaced by dry, deionized dimethylformamide (DMF). The resin is stored under DMF until used in the analysis.

To a 2.5-gram sample of polymer in 250 ml. of dry deionized DMF is added a small amount of a pH indicator comprising equal parts of 0.01% alcoholic solutions of Neutral Red and Xylene Cyanol FF indicators. The polymer solution is passed through the prepared resin column at a rate of about 10 ml. per minute. The resin bath is kept covered 'by liquid during this procedure, deionized DMF being used at the end to displace the last of the sample. The indicator serves to distinguish the acidic polymer solution from the pure DMF at both the beginning and the end of the sample emergence from the column.

A portion of the deionized polymer solution, in which the polymer now exists in the free acid form, is evaporated to dryness to determine solids content. Another portion is then titrated with standardized alcoholic potassium hydroxide to determine acidity, the added indicator now showing the titration end point. A simple calculation which compares this result with a blank experiment, wherein pure DMF replaces the polymer solution, establishes the meq./ kg. of acidity in the polymer sample. Neither component should have a combined anionic function of more than about 90 meq./kg., and preferably the combined anionic function of each component should be in the range of about 25 to meg/kg.

Among the addition monomers useful in this invention as exemplary of those which are non-ionizing in neutral media are methyl acrylate, methyl methacrylate, vinyl acetate, styrene, methacrylamide, methacrylonitrile, vinyl chloride, vinylidene chloride, methyl vinyl ketone and the like as well as any of the available vinyl pyridines. The latter class of comonomers is of special interest; under neutral modifiers, whice during exposure of the fiber to a pH below about 3 they act as bases, providing a useful degree of acid-dyeability. The preferred compounds include methyl acrylate, vinyl acetate, styrene and the vinyl pyridines.

Among the copolymeriza-ble sulfonates are the sulfonated styrenes, vinyl sulfonate, allyl sulfonate, methallyl sulfonate and their alkali-metal or alkaline-earth-metal salts, and the like, it being necessary only that the compound chosen from this class he copolymerizable with acrylonitrile to the desired extent. The preferred compounds are the sulfonated styrenes, it being understood that this designation includes their neutral salts.

While it is not intended that the invention be limited by a theoretical discussion, it will assist in understanding to consider current views of the probable basis for the unique crimp structure. It is highly probable that the values of two parameters, i.e., the ratio of maximum to minimum bending stiffness associated with a particular fiber cross-section and the ratio oftorsional rigidity to the lower bending stiffness, must be within certain ranges to permit this configuration. It will be seen that minor deviations from the maximum possible ratio of R/F can be introduced by textile processing of the fiber, but these effects are minor in relation to the torsional and bending characteristics referred to above.

EXAMPLES The examples which follow serve to illustrate the invention but are not to be construed as limitative. Percentages are by weight unless otherwise indicated.

Example I (A) Bicomponent acrylic fiber is spun from two solutions of the following compositions: Component A is produced from a 31.5% solution in dimethyl formamidc (DMF) of a tcrpolymer of 93.8% acrylonitrile, 6%

methyl acrylate and 0.2% sodium styrenesulfonate; Component B is produced from a 23.8% solution in DMF of a mixture of 90% polyacrylonitrile and of the terpolymer of component A. The terpolymer has an intrinsic viscosity of 1.5 and a combined anionic function of 55.6 meq./kg. The homopolymer has an intrinsic viscosity of 2.0 and a combined anionic function of 27 rneq./ kg. The solutions are spun using spinnerets such as described in the drawings, being fed at equal rates such that the weight ratio of polymeric component A to polymeric component B in the fiber is 58/42.

The filaments are spun into a hot, inert gas which flows concurrently therewith through an enclosure and serves to evaporate most of the solvent therefrom before the filaments are withdrawn. Filaments from a number of such spinning positions are accumulated to a tow of about 500,000 denier, comprising filaments of about 6.3 denier per filament exclusive of about solvent based on the total weight.

serves to extract the solvent to less than 2%, based on fiber weight. It is dried at 142 C. for 5 minutes and at 128 C. for 2.5 minutes in tow form after being mechanically crimped as in Example A. The final denier-per-filament is 6. Crimp analysis reveals retention of substantially all of the mechanical crimp, but development of little or no helical crimp. During a boil-off for minutes in water, the fiber develops 13.4 helical crimps/inch (5.3 /cm.) and is found to have an R/F of 0.03. Further data on this lot of fiber are given in Table 1.

(C) In an additional experiment, a sample of the product of A is tow-dyed in a standard manner and dried by passage over drums maintained at a surface temperature of 105 C. under a tension of about 75 mg./dcnier. This treatment substantially eliminates the crimp.

Tows of parts A, B and C are processed on the Pacific Convertor-worsted system to 2/ 13 worsted-count yarns. Crimp analyses are made at several stages as indicated in Table 1.

TABLE 1 Fiber from greige Fiber from tow spun yarn Fiber from mock-dyed ASAIS Boiled 01f As-is Boiled on Yarn Tow A:

R/F 1. 0 0. 98 0. 82 0. 67 0. 98 CI 15.2 10. 3 3. 2 9. 6 15. 2 F/in. (F/cm.) 38. 405. 2) 56. 2(22. 2) 43. 0(17. 0) 55. 6(22. 0) 38. 605. 2) Yarn CI* 20. 7 Tow B:

R/F 0. O3 0. 24 0. 39 0. 20 CI 5.9 13. 7 5. 7 6. 5 12. 5 F/in. F/cm.) 12. 6(5. 0) 13. 4 (5. 3) 11. 8(4. 7) 15. 3(6. 0) 15. 7(6. 2) Yarn 01* 26. 8 ow C:

R/F 0.46 0. 32 0. 29 0. 18 Yarn 01".... 25. 6

Method parallels that used for fiber.

The tow is passed through a series of water baths controlled at a temperature of 95 C. through which extraction liquor flows counter-currently to the tow path-oftravel. Fresh, hot water is continuously added to the final bath, and an aqueous solution of DMF is removed from the first for recovery of the solvent it contains. During passage through the extraction tanks, the tow is drawn, stepwise, to 193% of its as-spun length and the DMF is reduced to less than 2%, based on fiber weight.

The washed and drawn tow is lightly mechanically crimped in a stuifer-box crimper of the type described in the Hitt US. Pat. 2,311,174 which facilitates handling between crimping and drying.

The tow is distributed uniformly on the perforated belt of a continuous dryer and exposed to air heated to 140 C. for a period of 6.1 minutes and at a temperature of 135 C. for an additional 3.1 minutes. Due to high shrinkage while being dried, the final denier-per-filament is 6. The fiber exhibits a helical crimp of 38.4/ inch (15.2/ cm.) in which the ratio of crimp reversals to crimp frequency (R/F) is 1.0. The mechanical crimp is not apparent at this point. These and further data for this example are given in Table 1.

(B) By a process paralleling that of Example A except as noted, a bicomponent fiber is prepared to contain as one component a mixture of 85% polyacrylonitrile (of 2.0 intrinsic viscosity and a combined anionic function of 27 meq./kg.) and 15% of a copolymer of 96% acrylonitrile and 4% sodium styrenesulfonate (of 1.5 intrinsic viscosity and a combined anionic function of 260 meq./ kg.), and as the second the copolymer of the first. The 17.2 denier-per-filament fiber is drawn to 400% of its as-spun length in a series of water baths maintained initially at 93 C. and at 96 C. in the latter stages, which It will be seen that only the fiber of Tow A retains the crimp configuration of this invention during processing into yarn. The largely mechanical crimp of Tow B is modified to a helical crimp of low R/F value during boil-01f and never exhibits the desired high frequency of reversals at any stage. Tow C redevelops a helical crimp after removal by drawing, but is no longer exemplary of this invention.

Subjective evaluation of the yarns reveals good resilience and bulk in all three, with yarn B having a slight advantage over yarns A and C in these respects. Yarn A has a desirable crisp tactility, or bite, however, which is absent in Yarns B and C. Fabrics knitted from Yarns A and B confirm the impressions obtained from yarns evaluation. The crisp tactility of fabric from Yarn A is judged to be highly desirable. A reduced elasticity is seen in both Yarn A and fabric therefrom as compared with Yarns B and C and fabric from Yarn B. This difference is also reflected in the yarn crimp indices given in Table 1.

Example II The preparation of Example I(A) is repeated except that the tow is removed form the process prior to mechanical crimping. Upon drying under the conditions employed in that example, an equivalent R/F is obtained: [R/F, 0.97, CI, 16%, F, 28/inch (11/cm.)].

Example III The preparation of Example I(A) is repeated except for adjustment of spun denier, by means available in the art and drying at C. for 11.3 minutes, to yield a lower denier-per-filament after each of three drawratios as noted in Table 2. It will be seen that the crimp configuration characteristic of the fiber of this invention is present in all fibers regardless of the draw ratio employed.

This example illustrates the use of a copolymeric nonionizing modifier with acid-dyeing potential in the practice of this invention.

A bicomponent-fiber tow is prepared by the general procedure of Example I(A) to comprise, as one component, 85% of polyacrylonitrile (of 2.0 intrinsic viscosity and a combined anionic function of 27 meq./kg.) and 15% of a terpolymer of 88.9% acrylonitrile, 5.4% Z-methyl, -vinyl pyridine and 5.7% methyl acrylate [of 1.5 intrinsic viscosity and nil combined anionic function (polymer prepared by the process of the Milford and Wilkinson US. Patent No. 3,065,211, using an initiator which does not contribute ionic end groups)] and as the second component the terpolymer of the first. The spun denier-per-filament is 3.8. After extraction-drawing in an aqueous medium at 95 C. to 190% of its as-spun length, mechanically crimping and drying as tow at 150 C. for 11.3 minutes, the final denier-per-filament is 3.5. After boil-ofi" in water, the fiber properties are as follows: CI, 17.5, F, 46% in. (18.1/cm.), R/F, 0.94.

Example V This example illustrates the use of an alternative nonionizing copolymeric modifier in the practice of this invention.

Following the general procedure of Example I(A), a bicomponent-fiber tow is prepared in which one component comprises 90% polyacrylonitrile (of 2.0 intrinsic viscosity and a combined anionic function of 27 meq./ kg.) and of a terpolymer of 92.9% acrylonitrile, 6.7% vinyl acetate and 0.4% sodium styrenesulfonate (of 1.5 intrinsic viscosity and a combined anionic function of 65.4 meq./kg.) and as the second component the terpolymer of the first. The as-spun denier-per-filament is 3.6. After extraction-drawing in an aqueous medium at 75 C. to 212% of its as-spun length, mechanically crimping and drying at 150 C. for 11.3 minutes, the denier-perfilament is 3.4. Fiber properties after boil'olf are: CI, 19.3, F, 46.4/in. (18.3/cm.). R/F, as determined on fiber withdrawn from a finished, woven fabric prepared from the product of this example, is 0.94.

The following two examples are given for comparison; they are non-exemplary of this invention.

Example VI A bicomponent fiber is prepared by the general procedure of Example I(A) from the following components: Component A is a mixture of 90% polyacrylonitrile (of 2.0 intrinsic viscosity and a combined anionic function of 27 meq./kg.) and 10% of a terpolymer of 80.2% acrylonitrile, 19.2% vinyl acetate and 0.6% sodium styrenesulfonate (of 1.49 intrinsic viscosity and a combined anionic function of 44.7 meq./kg.) and the second component is the terpolymer of the first. After processing through drawing to 400% of its as-spun length and drying at 135 C. for 60 minutes, the fiber has a denier-per-filament of 3.8. On boil-01f in water, the fiber develops an intense helical crimp with infrequent crimp reversals.

Example VII A' bicomponent fiber is prepared to comprise as one component 100% polyacrylonitrile (of 2.0 intrinsic viscosity and a combined anionic function of 27 meq./kg.) and as the other a terpolymer of approximately 86.85% acrylonitrile, 12.7% vinyl acetate and 0.45% sodium styrenesulfonate (of 1.52 intrinsic viscosity and a combined anionic function of 66.4 meq./kg.). After extraction-drawing to 400% of its as-spun length and mechanically crimping, the tow is cut to 1.5-inch (3.8 cm.) staple and dried on a perforated tray for 30 minutes at 50 C. The final denier-perfilament is 3.6. After boil-off, the fiber is found to have an intense helical crimp in which the R/F value is 0.3.

The unique crimp structure of the fiber of this invention provides highly desirable aesthetics in fabrics constructed therefrom, as has been shown. It has also been found that the fiber of this invention confers an advantageous functionality to its fabrics in that they may be hang-dried without loss of shape. The fibers of substantial ionic differential known to the art (as exemplified in the Taylor US. Patent 3,038,237 and the Belck and Siedschlag US. Patent 3,039,524) provide excellent functionality in fabrics produced therefrom. It has been found, however, that best retention of shape through laundering requires tumbledrying to provide strain-free redevelopment of crimp. The fiber of this invention provides much of the functionality of the fibers of high ionic differential but may be dried in any manner Without objectionable loss of shape due to the durability of its unique crimp to wet conditions.

The bicomponent acrylic fibers of the Taylor and the Belck and Siedschlag patents referred to herein are characterized by the ability to squirm, i.e. to change in crimp intensity upon being subjected to hot-wet conditions but to regain their normal crimp frequency when dried and cooled. To a measureable extent the fiber of this invention also squirms. It has been found, however, that certain key structural-functional characteristics of a squirming fiber are absent in the fiber of this invention, primarily because substantially all the crimp of this fiber is developed before conversion to textile-spun yarns. This is of particular importance; it not only lowers the available stretch, but also prevents nesting, or follow-the-leader arrangement of the crimp in adjacent fibers, such as occurs when the crimp is developed to a major degree in the final yarn. These differences are reflected in an improvement in functionality of the present fiber as has been mentioned, namely essentially no loss in shape after washing and hang-drying.

Although for convenience and clarity of presentation this invention has been illustrated by fibers involving in one component polyacrylonitrile as one constituent, the invention is not so-limited. It is equally satisfactory to employ only copolymers in both components. It is only essential that the components have the limited ionic content and total modification specified and that they be produced in a cross-sectional shape which has no more than two axes of symmetry. The invention is intended to be limited only as set forth in the claims which follow.

What is claimed is:

1. A bicomponent acrylic fiber having a cross-section with no more than two axes of symmetry comprising two polymeric components:

(A) a copolymer consisting essentially of at least about 88% by weight acrylonitrile and up to a total of about 12% of both members of the group of copolymerizable compounds consisting of addition monomers which are non-ionizing in neutral media and addition monomers bearing sulfonate groups; and

(B) a mixture of polyacrylonitrile and a copolymer consisting essentially of at least about 88% by Weight acrylonitrile and up to a total of about 12% of both members of the group of copolymerizable compounds consisting of addition monomers which are non-ionizing in neutral media and addition monomers bearing sulfonate groups, said polymeric components each having no more than 90 milliequivalents per kilogram of combined anionic function, being present in a weight ratio in the range of :25 to 25:75 in the fiber-cross-section, said fiber having modi- 9 fied helical crimp in which the ratio of crimp reversals to crimp frequency (R/F) is in the range of 0.75 to 1.0.

2. The fiber of claim 1 wherein said polymeric components each have a combined anionic function of from about 25 to about 70 milliequivalents per kilogram.

3. The fiber of claim 1 wherein said addition monomers which are non-ionizing in neutral media are selected from the group consisting of methyl acrylate, vinyl acetate, styrene and vinyl pyridines, and wherein said addition monomers bearing sulfonate groups are sulfonated styrenes.

4. The fiber of claim 1 wherein said addition monomer which is non-ionizing in neutral media is methyl acrylate 10 and wherein said addition monomer bearing sulfonate groups is sodium styrene sulfonate.

References Cited UNITED STATES PATENTS 3,039,524 6/1962 Belck et a]. 161177 ROBERT F. BURNETT, Primary Examiner R. O. LINKER, JR., Assistant Examiner US. Cl. X.R. 161177 

